Data modeling question

From: <Rick_Cale_at_teamhealth.com>
Date: Wed, 30 Oct 2002 08:08:43 -0800
Message-ID: <F001.004F7803.20021030080843@fatcity.com>

I was reading one of the papers on the quest website about data modeling. An example was presented and I did not believe the results so I tried it out. Of course the writer ( Phd) was correct.

Does anyone know why does not enforce RI constraint if any of the foreign key colums are NULL. I took it literally that if I insert any record in table_2 that a corresponding record must be in the parent(table_1). Apparently this is not so. Someone please explain.

Thanks
Rick

drop table table_2;
drop table table_1;

create table table_1 (
  a number not null,
  b number not null,
  c number,
 constraint table_1_pk primary key (a,b));

create table table_2 (
a number,
b number,
d number not null,
e number not null,
f number,
constraint pk_table_2 primary key (d,e), constraint fk_table_2_reference_table_1 foreign key (a,b) references table_1 (a,b))
/

insert into table_2 values(1,NULL,3,4,5);

1 row processed.

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Author:
  INET: Rick_Cale_at_teamhealth.com

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